Sol–gel derived nanostructure hydroxyapatite powder and coating: aging time optimisation

The aim of this work was to evaluate the effect of aging time on the formation and phase purity of nanostructure hydroxyapatite powder and coating. Hydroxyapatite powder and coating were prepared by sol–gel method using calcium nitrate and phosphorous pentoxide as starting materials. Precursor sols were dip coated onto the pure titanium substrates. The coated plates were aged in different aging times and dried. Finally, samples were calcinated at 600 and 700°C. Thermal behaviour, phase formation, surface morphology and interfacial coherency were investigated by thermogravitometry analysis, X-ray diffraction and scanning electron microscope. Results showed that a solution aging time of at least 24 h was required to achieve monophasic nanostructure hydroxyapatite powder and coating. Hydroxyapatite structure of coating was obtained at 600°C, and a β-tricalcium phosphate phase was formed at 700°C. The effect of sintering temperatures on crystallite size of the coatings was not significant.